This invention relates to a method and apparatus for making a molded article having a field of integrally molded hooks formed on at least one surface thereof. This invention further relates to such a method and apparatus wherein a surface of the article bearing a field of integrally molded hooks could experience shear forces as the article is removed from the mold.
An injection molded article having a field of hooks formed integrally on a surface thereof and a method and apparatus for making such an article are disclosed in U.S. Pat. Nos. 5,656,226 and RE 37,338, the disclosures of which are incorporated herein by reference in their entireties. As disclosed in these references, an injection molded article has a field of injection molded hooks integrally formed on a predetermined area thereof on at least one wall during the injection molding process, the field of hooks capable of releasable attachment to a cooperative loop-bearing member. The hooks have reduced radius compared to prior art hooks and a changed geometry for promoting ejection from the mold during the injection molding process, yet still maintain the desired fastening function. The thermoplastic material used to mold the hooks has a memory sufficient to cause the hooks to return substantially to their original position after being removed from the mold, and yet has sufficient flexibility to allow the hooks to bend during removal from the mold and during engagement and release from the cooperative loop-bearing member.
As further disclosed in the references, an apparatus for making such a molded article can comprise a mold block having two sections that join together to define a cavity having the shape of the injection molded article. A recess is formed in the mold block for receiving an insert, the insert comprising plates each having hook-shaped cavities formed in an edge thereof, such that when the plates are placed in stacked relation their edges define a field of hook shaped cavities, the plate edges defining one surface of the mold insert that can be substantially contiguous with the inner surface of a section of the mold block. The plates having the hook-shaped cavities can be alternated with spacer plates having no cavities to define a field of spaced rows of hooks formed on a surface of the molded article.
In the embodiment illustrated in the references, the injection molded device is an orthopedic ankle brace, and in particular one of the shells of the brace that are disposed on either side of a patient's ankle. The field of hooks are formed on a surface of the shell, such that when the mold block is opened and the molded article is removed, the article is lifted off the mold section such that there is little or no shear experienced by the molded field of hooks, that is, the base of the field of hooks is formed on a wall of the molded article that is substantially normal to the direction in which the molded article is removed from the mold cavity. The hooks may temporarily straighten as the article is removed from the mold and the hooks are withdrawn from the insert, but the hooks almost immediately return to substantially their original shape.
In other embodiments of injection molded devices, however, the device may need to be lifted off or out of the mold in a manner such that the base of the field of hooks would not be withdrawn in a direction substantially normal to the hook-forming surface of a mold insert. The method and apparatus of U.S. Pat. Nos. 5,656,226 and RE 37,338 can be used in the molding of articles in which the draft angle experienced by the surface of the molded article bearing the field of injection molded hooks is greater than about 45°, depending on the thermoplastic material being molded. At a draft angle less than about 45°, the field of hooks can experience shear forces that can damage the hooks as they are removed from the mold. This would be the case if a wall of the finished article lies in a plane more parallel than perpendicular to the direction in which the article is withdrawn from the mold For example, if the article to be injection molded is in the shape of a box or container, and the field of hooks is to be formed on an inner or outer side surface of the box, then when the molded box is withdrawn from the mold, the field of hooks could experience shear forces. These shear forces could be damaging to the field of injection molded hooks.
U.S. Pat. No. 6,224,364, assigned to Velcro Industries, B.V. discloses an injection molded product having an array of fastener elements integrally molded with the product, the product being molded in a closed cavity die, at least one of the parts of the die having a movable segment constructed to be retracted across the mold cavity, such that the fastener element cavities and the mold cavity can be filled under different filling conditions and molded under different conditions.
It is thus one object of the invention to provide a molded article having a field of integrally molded hooks thereon wherein the base of the field of the integrally molded hooks has a draft angle less than about 45° as the article is withdrawn from the mold.
It is another object of the invention to provide a method and apparatus for making a molded article having a field of hooks on one surface thereof, wherein the base of the field of hooks has a draft angle less than about 45° as the direction in which the article is withdrawn from the mold.